I was reading that ants will kill worms off, so this got me wondering is there such a thing as ant castings since I've found that a type of stinging ants love to move into wood chip piles.
Well yes, they excrete like all animals, and yes this would contain nutrients. You are unlikely to see that though as they are quite fastidious creatures and like to do their own composting.
You may sometimes see granular material that they have deposited around the entrances to their nest, but this is just material that they have excavated.
In an open compost heap or in the soil things tend to keep themselves in check, so I wouldn't worry too much.